Cold sensitive and heat sensitive mutants of Saccharomyces cerevisae which become reversibly defective in mitochondrial function at the nonpermissive temperature (18 degrees or 37 degrees C) will be used in genetic and biochemical analyses to elucidate the sequence of events involved in the growth and differentiation of mitochondrial membranes. The broad goals of the research program are: 1) to determine the extent to which membrane biogenesis depends on an ordered pathway of biosynthetic and assembly steps; (2) to ascertain the cellular location of the genetic determinants controlling these processes; and 3) to define at the molecular level the sequence of biochemical events leading to the formation of fully functional membrane-bound enzyme complexes.